Fabrication of new glass-ceramic materials from float glass and slag waste by modulation of the cooling rate.

This study explores an alternative route to recycle waste materials from float glass (FG, 30 wt%) and copper slag (CS, 70 wt%). The FG is a silica-rich glass, while the CS is rich in Fe and Zn. They were melted at 1550 °C to obtain a homogeneous glass that was then re-melted and cooled at 10 (low) and 500 (high) °C/h to produce a glass-ceramic. X-Ray Powder Diffraction, Scanning Electron Microscope and Electron microprobe characterisations show that both products contain spinel crystals within an abundant glassy matrix. At 500 °C/h, unexpectedly, the glass-ceramic contains a higher content (30.0 ± 5.5 area%) of tiny and long dendrites (spinifex) of spinels than at 10 °C/h (13.7 ± 2.2 area%); at the low rate, spinels are skeletal (large crystals) to dendritic (tiny and short) and larger than at high rate. This unveils that the estimated crystal growth rate (10-7 cm/s) is higher at 500 °C/h. The crystal-chemistry of spinels results in more enriched Fe and Zn at 10 °C/h than at the high rate. This approach is promising for various applications or for concentrating valuable transition metals (Fe, Zn) as a function of cooling rate and type and quantity of starting waste materials; also, it avoids treatments with additives or fluxing agents and it provides, thanks to the dielectric properties shown, a strong potential for industrial use as a microwave absorber.